Unit 2 skeletal system pt 2

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Questions and Answers

What is the primary function of osteoblasts in bone formation?

To maintain bone tissue

To convert fat into red marrow

To produce new bone matrix (correct)

To stimulate bone resorption

Which type of bone tissue is characterized by dense and hard structures?

Bone marrow

Cancellous bone

Fibrous bone

Compact bone (correct)

What role do osteocytes play in the bone matrix?

They create new osteons

They transport nutrients to bone marrow

They maintain and monitor bone tissue health (correct)

They are responsible for initiating bone remodeling

What is the significance of the periosteum in bone anatomy?

It provides a protective layer and supports vessels and nerves Signup and view all the answers

How does the body regulate calcium levels in relation to bone tissue?

Through hormonal control affecting osteoclast and osteoblast activity Signup and view all the answers

What role does parathyroid hormone (PTH) play when calcium levels are low?

Increases serum calcium levels by stimulating osteoclasts Signup and view all the answers

Which factors are likely to trigger early bone-forming cells (osteoblasts) to start developing?

Osteoclast signals and local mechanical strain Signup and view all the answers

What is the primary purpose of coupling in bone remodeling?

To achieve balance between bone absorption and formation Signup and view all the answers

What type of cells help prepare for new bone formation on the bone surface?

Reversal cells Signup and view all the answers

Which of the following is a matrix-derived factor that influences bone formation?

Insulin-like growth factors Signup and view all the answers

Which of the following bone cells is primarily responsible for breaking down bone?

Osteoclasts Signup and view all the answers

How does calcitonin function when calcium levels are high?

Inhibits osteoclast activity Signup and view all the answers

What is the main influence of osteoclast secreted factors?

Reducing bone resorption without affecting formation Signup and view all the answers

Which of the following best describes the role of osteoprogenitor cells?

They can differentiate into various cell types. Signup and view all the answers

What is the primary function of osteoblasts?

To convert osteoids to mature mineralized bones. Signup and view all the answers

During bone remodeling, which cells are primarily responsible for the reabsorption of mineralized bone?

Osteoclasts Signup and view all the answers

What type of bone tissue is characterized by an arrangement in trabeculae and irregular holes?

Spongy (cancellous) bone Signup and view all the answers

Which of the following components makes up the bone matrix?

Calcium and phosphate minerals Signup and view all the answers

Which type of bone is primarily composed of spongy bone and has a cube-like shape?

Short bones Signup and view all the answers

What is the zone of proliferation's role in the epiphyseal plate?

It is responsible for longitudinal growth. Signup and view all the answers

Which of the following cells is most abundant in mature bone?

Osteocytes Signup and view all the answers

The process by which osteoblasts and osteoclasts work together is important for which of the following?

Calcium regulation Signup and view all the answers

What structural component do compact bones primarily consist of?

Haversian systems (osteons) Signup and view all the answers

Study Notes

Spongy Bone

Composed of bars and plates called trabeculae
Spaces between trabeculae contain red bone marrow, which produces red blood cells

Bone Cells

Osteoprogenitor Cells: Non-specialized cells found in periosteum, endosteum, and central canal of compact bones. They can turn into other cell types as needed.
Osteoblasts: Responsible for building osteoids. They mature from mesenchymal stem cells and are regulated by parathyroid hormone and vitamin D.
Osteocytes: Most abundant bone cell. They connect via tunnels called canaliculi, which allow for communication and nutrient/waste transport. Osteocytes are responsible for mechanosensing and responding to strain.
Osteoclasts: Responsible for reabsorbing mineralized bone by pumping carbonic acid and enzymes. They are activated by osteoblast activity, which is important for calcium regulation.
Bone Lining Cells: Old osteocytes that no longer play a role in synthesis. They are flat and thin with little activity. When the bone lining cell peels back, it stimulates osteoclasts for resorption.

Bone Matrix

Osteoid: Immature bone matrix not yet mineralized.
Bone Collagens: Bone is mostly type 1 collagen which gives it a rigid structure.
Extracellular Matrix: Mostly made of mineral (calcium and phosphate), which gives bone it’s its mechanical properties.

Bone Types

Long Bones: Long shaft with two bulky ends composed predominantly of compact bone with spongy bone at the ends. They have three distinct zones:
- Epiphysis: Region at the end of the bone, which allows for attachment at joints.
- Metaphysis: Transitional area where most tendons attach.
- Diaphysis: Center region that provides structural function.
Short Bones: Formed similarly to long bones but vary in shape and size. They are cube-shaped and primarily composed of spongy bone.
Flat Bones: Have a cortical shell and stiff interior. They are broad and flat, providing protection or a flat surface for attachments.
Irregular Bones: Primarily composed of spongy bone like the bones of the spine.

Compact and Spongy Bone

Compact Bone: Dense and strong tissue that makes up the outer cortex. It’s composed of osteons (Haversian System).
Spongy Bone (Cancellous): Composed of trabeculae (instead of Haversian System). It is lined with endosteum and makes bone lighter, providing space for red bone marrow.

Gross Bone Anatomy

Diaphysis: Medullary cavity filled with bone marrow and outer wall composed of dense hard compact bone.
Epiphysis: Filled with spongy bone and covered by hyaline cartilage.

Bone Anatomy

Periosteum: Tough and fibrous tissue covering bone that provides attachment points for ligaments. It also contains blood vessels, lymph vessels, and nerves.
Bone Marrow:
- Red Marrow: Produces blood cells
- Yellow Marrow: High in fat and can convert to red marrow in an emergency.

Blood and Nerve Supply

Arteries enter through the nutrient foramen, serving the spongy bone and medullary cavity.
Nerves follow similar pathways.

Calcium Homeostasis

Regulated by PTH, Vitamin D, and Calcitonin.
- Low Calcium: Parathyroid hormone (PTH) increases serum calcium levels by:
  - Increasing kidney’s ability to convert Vitamin D into its active form
  - Stimulating osteoblasts, which upregulates osteoclasts
- High Calcium: PTH is downregulated and calcitonin is released to downregulate osteoclasts.

Coupling and Remodeling

The role of coupling and remodeling is to keep bone strong and heal damage.
Dual Regulation: Coupling is regulated locally by mechanical strain and a variety of proteins, and systemically by Vitamin D, PTH, and calcitonin.
Uncoupling: When the need for serum calcium levels outweighs the need for coupling, bone absorption and formation are uncoupled to reach homeostasis.

Coupling Signals

Matrix Derived Factors: The bone matrix stores growth factors including platelet-derived growth factor and insulin-like growth factors, which are deposited by osteoblasts and released by osteoclasts. These factors mainly stimulate osteoblast progenitors.
Osteoclast Secreted Factors: Contain anti-resorptive inhibitors that may reduce bone resorption without impacting bone formation.
Osteoclast Membrane Bound Factors: Osteoclasts interact directly with mature osteoblasts to promote their activity.

Coupling Mechanisms

Bone breakdown (resorption) and bone formation are linked, even though they don’t happen at the same time.
Mechanism 1: Osteoclasts release signals that trigger early bone-forming cells (osteoblasts) to start developing. Other signals from nearby cells in the bone unit fine-tune the number and activity of bone-forming cells.
Mechanism 2: Other cells help pass along these signals to both developing and mature osteoblasts, including:
- Cells that are already in the osteoblast family and are located in the protective layer over the remodeling bone.
- Reversal cells, which are found on the bone surface and help prepare for new bone formation.
- Osteocytes, which are mature bone cells embedded in the bone that help communicate about bone changes.

Objectives

Compare and contrast osteoblasts and osteocytes.
Identify major long, short, flat, and irregular bones in the body.
Describe the process of calcium regulation in the body.

Bird’s Eye View

Bones are the scaffolding of the body, performing many functions:
- Providing shape
- Allowing for motion
- Protecting organs
- Cell production in bone marrow
An adult has about 206 bones.

Basic Bone Anatomy

Periosteum: Tough and fibrous connective tissue that covers bone.
- Contains blood vessels for nutrient transport.
- Contains lymph vessels and nerves.
- Acts as an anchor point for ligaments and tendons.
Epiphysis: End of a long bone.
Diaphysis: Region between the epiphyses.
- Medullary cavity: Hollow within the diaphysis that stores yellow marrow.
- Yellow marrow: High in fat content and can convert to red marrow (which makes red blood cells) in an emergency.

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